Polymeric composite materials and methods of making them

ABSTRACT

Disclosed are processes for making polymeric composite materials and composite materials made from those processes the process comprising: providing a mixture, comprising: a liquid, a polymer precursor, and a dispersed-phase precursor; and subjecting the mixture to reaction conditions sufficient: to effect polymerization of the polymer precursor to produce a polymer and a reaction product; and to remove substantially all the liquid and reaction product from the mixture; wherein said reaction conditions comprise: pressure between about 10 millitorr and about 300 torr; and temperature: greater than or equal to the highest boiling point of the liquid and reaction product; less than the decomposition temperature of the polymer; and less than the decomposition temperature of the dispersed-phase precursor.

TECHNICAL FIELD

The invention relates to processes for making polymeric compositematerials and composite materials made from those processes.

BACKGROUND

Conventional methods of achieving well dispersed blends of inorganicmaterial or cellulose fiber in a polymer matrix include simple mixing,high shear mixing (as developed in a Kady mill or Cowles mixer, or ahigh pressure homogenizer) or through the use of dispersants. With suchmethods, it can be difficult to disperse inorganic particles or fibrousmaterials uniformly throughout the polymer matrix. For example, the highwater content and hydrophilic nature of nanocellulose makes it difficultto disperse this material in many polymeric systems, such as plasticsand other hydrophobic composites. Additionally, it can be difficult withexisting methods to produce a high solids dispersion of some materials.For example, it is difficult with existing methods to achieve greaterthan 3% solids content of nanocellulose in a water-based slurry andstill have a slurry that flows or can be pumped. Similarly, it isdifficult with existing methods to achieve greater than 70-72% solidscontent of inorganic materials in an aqueous slurry that is stillpumpable.

SUMMARY

There remains a need for methods of making polymeric composite materialsthat permit a higher degree of dispersion of and/or a high concentrationof a dispersed phase than is possible with existing methods.

In one aspect, the invention is directed to a method of producing acomposite material having a matrix and a dispersed phase, comprising:(A) providing a mixture, comprising: (i) a liquid; (ii) a polymerprecursor; and (iii) a dispersed-phase precursor; and (B) subjecting themixture to reaction conditions sufficient: (i) to effect polymerizationof the polymer precursor to produce a polymer and a reaction product;and (ii) to remove substantially all the liquid and reaction productfrom the mixture; wherein said reaction conditions comprise: (a)pressure between about 10 millitorr and about 300 torr; and (b)temperature: (i) greater than or equal to the highest boiling point ofthe liquid and reaction product; (ii) less than the decompositiontemperature of the polymer; and (iii) less than the decompositiontemperature of the dispersed-phase precursor; whereby the matrixcomprises the polymer, and the dispersed phase comprises thedispersed-phase precursor dispersed within the matrix.

In one aspect, the invention is directed to a method comprising:producing a composite material having a matrix and a dispersed phase,comprising: (A) providing a mixture, comprising: (i) a liquid; (ii) apolymer precursor; and (iii) a dispersed-phase precursor; and (B)subjecting the mixture to reaction conditions sufficient: (i) to effectpolymerization of the polymer precursor to produce a polymer and areaction product; and (ii) to remove substantially all the liquid andreaction product from the mixture; wherein said reaction conditionscomprise: (a) pressure between about 10 millitorr and about 300 torr;and (b) temperature: (i) greater than or equal to the highest boilingpoint of the liquid and reaction product; (ii) less than thedecomposition temperature of the polymer; and (iii) less than thedecomposition temperature of the dispersed-phase precursor; whereby thematrix comprises the polymer, and the dispersed phase comprises thedispersed-phase precursor dispersed within the matrix; and furthercomprising treating the composite material with a cross-linking agent.

In one aspect, the invention is directed to a composite material havinga matrix and a dispersed phase, produced by a process comprising: (A)providing a mixture, comprising: (i) a liquid; (ii) a polymer precursor;and (iii) a dispersed-phase precursor; and (B) subjecting the mixture toreaction conditions sufficient: (i) to effect polymerization of thepolymer precursor to produce a polymer and a reaction product; and (ii)to remove substantially all the liquid and reaction product from themixture; wherein said reaction conditions comprise: (a) pressure betweenabout 10 millitorr and about 300 torr; and (b) temperature: (i) greaterthan or equal to the highest boiling point of the liquid and reactionproduct; (ii) less than the decomposition temperature of the polymer;and (iii) less than the decomposition temperature of the dispersed-phaseprecursor; whereby the matrix comprises the polymer, and the dispersedphase comprises the dispersed-phase precursor dispersed within thematrix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a low-magnification (81×) scanning electron microscopy (SEM)image of a surface of paper coated with coating A according to Example2.

FIG. 2 is a low-magnification (81×) scanning electron microscopy (SEM)image of a surface of paper coated with coating B according to Example2.

FIG. 3 is a high-magnification (183×) scanning electron microscopy (SEM)image of a surface of paper coated with coating A according to Example2.

FIG. 4 is a high-magnification (183×) scanning electron microscopy (SEM)image of a surface of paper coated with coating B according to Example2.

FIG. 5A is an image of paper coated with a starch and polyvinyl alcoholcoating and a silicone coating, after stain testing, according toExample 4

FIG. 5B is an image of paper coated with a PLA/Clay composite coatingand a silicone coating, after stain testing, according to Example 4.

DETAILED DESCRIPTION

In some embodiments, the invention is directed to a method of producinga composite material having a matrix and a dispersed phase, comprising:

-   -   (A) providing a mixture, comprising:        -   (i) a liquid;        -   (ii) a polymer precursor; and        -   (iii) a dispersed-phase precursor;    -   and    -   (B) subjecting the mixture to reaction conditions sufficient:        -   (i) to effect polymerization of the polymer precursor to            produce a polymer and a reaction product; and        -   (ii) to remove substantially all the liquid and reaction            product from the mixture; wherein said reaction conditions            comprise:        -   (a) pressure between about 10 millitorr and about 300 torr;            and        -   (b) temperature:            -   (i) greater than or equal to the highest boiling point                of the liquid and reaction product;            -   (ii) less than the decomposition temperature of the                polymer; and            -   (iii) less than the decomposition temperature of the                dispersed-phase precursor;    -   whereby the matrix comprises the polymer, and the dispersed        phase comprises the dispersed-phase precursor dispersed within        the matrix.

The liquid can be any liquid suitable for use with the polymer precursorand dispersed-phase precursor under the conditions of the methods. Theliquid can be used to aid in spreading the polymer precursor over largequantities of dispersed inorganic material prior to undergoing recation.Suitable liquides include water, waxes, fatty acids, polyamides,polyesters and the like. In some embodiments, the liquid is water.

The temperature refers to the temperature of the mixture. In someembodiments, the temperature is between about 70° C. and about 200° C.In some embodiments, the temperature is between about 120° C. and about170° C. If a correlation between the temperature of the mixture and adifferent temperature (e.g., of the reaction vessel, of the atmospherewithin the reaction vessel) is established, it is possible to monitorthe temperature of the mixture using this surrogate temperature.

In some embodiments, the pressure is between about 10 millitorr andabout 250 torr. In some embodiments, pressure is between about 10millitorr and about 50 torr. In some embodiments, the pressure isbetween about 10 millitorr and about 1 torr.

In some embodiments, the temperature is between about 120° C. and about170° C.; and the pressure is between about 10 millitorr and about 1torr.

The boiling point of the liquid and reaction product refers to theboiling point at the pressure of the reaction conditions. When more thanone liquid is present, it refers to the highest boiling point of anyliquid present. Where appropriate, it refers to an azeotrope between twoor more liquids. The reaction product will typically be a small moleculethat is a liquid (under ambient conditions). In some embodiments, thereaction product is water. In some embodiments, the reaction product ismethanol. In some embodiments, the reaction product is ethanol. In someembodiments, the reaction product is peroxide. In some embodiments, boththe liquid and the reaction product are water.

The polymer precursor can be any substance (such as a monomer) capableof undergoing polymerization (e.g., via condensation) under theconditions of the methods of the invention.

In some embodiments, the polymer precursor is an organic acid. In someembodiments, the organic acid is lactic acid, itaconic acid or citricacid.

The dispersed-phase precursor can be any substance capable of beingdispersed throughout the matrix under the conditions of the methods ofthe invention. For example, when the polymer precursor is an organicacid, substances that react with acids (e.g., basic substances such ascalcium carbonate) are not suitable.

In some embodiments, the dispersed-phase precursor is an inorganicmaterial. In some embodiments, the inorganic material is clay, talc,aluminum trihydrate, barium sulfate, a metal oxide or a silicate.Silicates include oxides (e.g., quartz family) and alumino-silicates(e.g., zeolites, benonites). In some embodiments, the inorganic materialis clay. In some embodiments, the metal oxide is titanium dioxide orantimony oxide. In some embodiments, the silicate is analumino-silicate.

In some embodiments, the dispersed-phase precursor is a fibrousmaterial. In some embodiments, the fibrous material is wood fiber, flax,cotton, hemp, jute, nanocellulose, rayon, polyester, nylon, aramidfibers, rock wool, mineral wool, asbestos or fiberglass. In someembodiments, the fibrous material is nanocellulose.

In some embodiments, the invention is directed to a method of producinga composite material as described above, and further treating thecomposite material with a cross-linking agent.

In some embodiments, the cross-linking agent is ammonium zirconiumcarbonate, potassium zirconium carbonate, a glyoxal, an aliphatic epoxyresin, a melamine formaldehyde resin or a blocked isocyanate. In someembodiments, the cross-linking agent is ammonium zirconium carbonate,potassium zirconium carbonate or glyoxal.

In some embodiments, one or more additional components are blended withthe mixture as the composite material is being formed, when theconditions of hydrophobicity, pH, viscosity, etc. are advantageous. Thiscan be during polymerization, or after the polymerization reaction isessentially complete. Advantageously, this permits the addition ofmaterials to the composites that would otherwise be very difficult to door that are inherently incompatible with the composite in its final form(e.g., a hydrophilic cellulose fiber or hydrous clay into a hydrophobic,high viscosity polymer matrix).

In some embodiments, the mixture is blended with a light-scatteringcompound. In some embodiments, a light-scattering compound changes thelight-scattering coefficient (s) of the material to which it is added byabout 10 cm²/g or more. In some embodiments, the mixture is blended witha light-absorbing compound. In some embodiments, a light-absorbingcompound changes the light-absorption coefficient (k) of the material towhich it is added by about 0.1 cm²/g or more. The coefficients s and kare to be understood in terms of Kubelka-Munk theory as described in theTechnical Association of Pulp and Paper Industries (TAPPI) StandardPractice T 1214 sp-12 “Interrelation of reflectance, reflectivity; TAPPIopacity; scattering and absorption.”

In some embodiments, the mixture is blended with a fluorescent compound.In some embodiments, a fluorescent compound is an Optical BrighteningAgent (OBA), i.e, a dye that absorbs energy in the uv portion of theelectromagnetic spectrum and emits energy in the visible light portion.In some embodiments, an OBA increases the TAPPI Brightness (measuredaccording to T-452) of the material to which it is added by about 0.2points or more.

In some embodiments, the mixture is blended with a low-density material.A low-density material has a specific gravity less than the polymer ofthe composite. In some embodiments, a low-density material is hollowplastic pigment, vermiculite or pearlite.

The methods of the invention are capable of producing compositematerials with a higher dispersed phase concentration, a lower viscosityand/or a higher degree of dispersion and/or distribution than ispossible with existing methods.

In some embodiments, the composite material has a weight concentrationof nanocellulose of 5%, 6%, 7%, 8%, 9%, 10% or higher (e.g., 15%, 20%,25%, 30%, 40% or 50%). In such a material, the nanocellulose is welldispersed and the composite material is easily pumped. The high solidsdispersion of nanocellulose presents an expanded opportunity toincorporate sufficient fractions of the material into paper coating,paints and composites to improve properties of these materials.

In addition to the high degree of particle dispersion in the composite,these embodiments also have the advantage of improved compatibility ofnanocellulose when used as a reinforcing agent in hydrophobic systemssuch as high molecular weight polylactic acid, polyethylene,polypropylene, and other plastics and composites.

In some embodiments, the composite material has a weight concentrationof clay of 75%, 77%, 79% or 80%. In such a material, the clay is welldispersed and the composite material is easily pumped.

In the case of a high aspect ratio clay and lactic acid, a compositeproduced using the methods of the invention results in a well dispersed,high solids material with oligomer chemically reacted onto the surfaceof the clay. The elevated temperature and low pressure conditions thatdrive off the water present in the solution of lactic acid, the clayslurry and the water formed during the condensation reaction also drivesoff the layer of water strongly absorbed onto the surface of the clay,exposing a highly reactive mineral surface that reacts with the lacticacid, forming a highly stable chemical bond between the oligomer and thesurface of the clay. Evidence of this chemical bond is demonstrated bythe improved solvent resistance of the polymeric composite compared tothat of a simple admixture of the same polylactic acid oligomer andclay, as demonstrated in Example 1.

Binder migration in paper coatings, which takes place during the coatingdrying process, can lead to print quality problems. The chemical bondbetween the oligomer and the surface of clay particles in a compositeproduced by the methods of the invention immobilizes the compositewithin the coating layer when used as a coating binder. This minimizesbinder migration during the drying of a coating and overcomes alimitation of conventional paper coating binders.

The high solids composite can be used as a binder in paints andcoatings, replacing higher cost, non-biodegradable petroleum-based latexbinders. The composite can also be used as a reinforcing agent inplastics and other composites. The composite can be cross-linked, usingcompounds such as AZC, KZC or glyoxal, further enhancing its binding andreinforcing properties.

The compositions produced by this method have been demonstrated to beuseful as a coating for paper, wood, cloth, metal, plastic, film orfoil. As shown in Example 2, the reaction between the polymer anddispersed phase material produces a composite that promotes improvedcoverage of the substrate compared to a composite made by simplyblending the polymer and dispered phase materials together.

EXAMPLES Example 1

This example demonstrates the improved chemical resistance of thecomposite material produced according to the methods of the invention.

Three composites, labeled Composite A-C, were produced according to themethods of the invention by blending a polymer precursor and variousdispersed-phase precursors, in accordance with Table 1, and subjected toa temperature of 150° C. and a step-wise decrease in pressure fromatmospheric pressure to 28 torr until substantially all of the water wasremoved. A fourth composite, Composite D, is a simple mixture ofpolylactic acid polymer blended, but not reacted with, talc.

TABLE 1 Compositions prior to methylene chloride extraction. Com-Polymer Precursor Dispersed Phase Precursor posite Identity Amount (gms)Identity Amount (gms) A lactic acid 5.623 talc 13.120 B lactic acid5.588 dispersed clay 13.038 C lactic acid 4.778 non-dispersed clay11.148 D lactic acid 9.070 talc 9.072

The composites were then refluxed with methylene chloride for four hoursand the composition of the resulting residual was determined analyzed byadapting Tappi standard method T211 om-85 “Ash in wood and pulp”. Thecomposition of the resulting material is presented in Table 2 below foreach composite described in Table 1.

TABLE 2 Compositions following methylene chloride extraction. PolymerPrecursor Dispersed Phase Precursor Amount Amount Polymer CompositeIdentity (gms) Identity (gms) Extracted A lactic acid 1.042 talc 12.80081% B lactic acid 1.124 dispersed clay 13.020 80% C lactic acid 1.321non-dispersed 11.102 72% clay D lactic acid 0.000 talc 8.412 100%

Polylactic acid is soluble in methylene chloride. As shown in Table 2,Composites A, B and C, produced according to the methods of theinvention, demonstrated a significant resistance to dissolution by themethylene chloride solvent compared to Composite D, a mixture ofpolylactic acid polymer blended, but not reacted with, talc.

Example 2

This example demonstrates the improved substrate coverage for thecomposite material of the invention.

Two coatings of similar composition, designated A and B, were prepared.Coating A was prepared according to the methods of the invention(labeled as “reacted” in Table 3, below). Coating B is a blended(non-reacted) composition. The composition of the coatings is shown inTable 3.

TABLE 3 Coating Compositions. Dispersed Polymer Precursor PhasePrecursor Coating Method Identity % wt Identity % wt A Reacted lacticacid 96 nanocellulose 4 B Blended lactic acid 96 nanocellulose 4

A paper coating substrate with a nominal basis weight of 32 grams perm², typical of light weight packaging papers, was coated with coatings Aand B using a standard laboratory coating draw-down method. The coatingswere applied at a coatweight of approximately 10 grams per m², asdetermined gravimetrically.

Scanning electron microscope images were taken of the coated papersurfaces as shown in FIG. 1-4. The microphotographs clearly show theimproved substrate coverage for the composition of the inventioncompared to the similar composition which was blended.

Example 3

A flooded nip size press is often used to apply sizing or a surfacecoating to a broad range of paper grades, including printing and writingand packaging grades. One of the benefits of this coating application isto seal the surface of the paper, thereby improving print quality and/orreducing air porosity.

This type of coating application method is limited to low viscositycoating formulations (less than 700 cps Brookfield viscosity) to preventcoating rejection at the nip and poor coating coverage. For starch-basedcoating formulations, this limits coating solids to 15% solids or lessand, therefore, the level of coat weight that can be applied to thesurface of the paper.

A nominal 38 gsm uncoated paper, made from bleached chemical pulp, wascoated on the pilot paper machine at the University of Maine using aconventional, inclined, flooded nip size press. A typical 96 wt % starchand 4 wt % polyvinyl alcohol coating formulation at 15% solids was usedas the control coating and compared to a coating containing apoly-lactic acid (PLA)/Clay composite, made by the method of theinvention, at 54% solids. Both coating formulations exhibited similarviscosities and both performed well on the coater. As shown in Table 4,the results of the paper testing shows that the PLA/Clay composite wasmuch more effective in developing low air permeability compared to thestandard starch/PVA formulation.

TABLE 4 Coated Paper. Gurley Porosity, sec Sample (for 100 cc air)Coating % solids Uncoated Base Paper 17.3 N/A Base Paper with Control21.8 15.1% Coating Base Paper with PLA/Clay 222 54.1% coating

Example 4

A release base paper grade was produced using the pilot paper machine atthe University of Maine with a nominal basis weight of 80 gm/m². Thefiber furnish was 70% northern bleached hardwood kraft and 30% northernbleached softwood kraft, refined to a freeness of 200 ml CanadianStandard Freeness. Cellulose nanofibrils and cooked corn starch wereblended together and added to the furnish at a rate of 200 lb/ton offiber. The pH of the wet end was maintained at approximately 7 and nofiller was added to the furnish.

An inclined size press was used to apply two separate size press coatingformulations to the basepaper. The first formation was a blend of 96 wt% starch and 4 wt % polyvinyl alcohol and the second coating formulationwas a 70% PLA and 30% Clay novel composite material produced accordingto the invention. Both sets of papers were then calendared using a hot,soft nip calendar with 3000 pli of pressure and a roll surfacetemperature of 200 F.

Both papers were then silicone coated with 0.71 lb of silicone/3000 ft²of paper. A test ink was applied to the surface of the paper and theunabsorbed ink wiped with a cloth. The ink that penetrated into thestructure of the paper remained leaving a dark stain pattern in the testsample.

FIG. 5A is an image of the starch/PVA coated samples after the teststain was applied to the surface and wiped clean. FIG. 5B is an image ofthe PLA/Clay coated paper sample after the ink stain test. A comparisonof the two test samples shows the improved barrier properties for thePLA/Clay composite coated sample compared to the starch/PVA coatedpaper.

1. A method of producing a composite material having a matrix and adispersed phase, comprising: (A) providing a mixture, comprising: (i) aliquid; (ii) a polymer precursor; and (iii) a dispersed-phase precursor;and (B) subjecting the mixture to reaction conditions sufficient: (i) toeffect polymerization of the polymer precursor to produce a polymer anda reaction product; and (ii) to remove substantially all the liquid andreaction product from the mixture; wherein said reaction conditionscomprise: (a) pressure between about 10 millitorr and about 300 torr;and (b) temperature: (i) greater than or equal to the highest boilingpoint of the liquid and reaction product; (ii) less than thedecomposition temperature of the polymer; and (iii) less than thedecomposition temperature of the dispersed-phase precursor; whereby thematrix comprises the polymer, and the dispersed phase comprises thedispersed-phase precursor dispersed within the matrix.
 2. The methodaccording to claim 1, wherein the temperature is between about 70° C.and about 200° C.
 3. (canceled)
 4. The method according to claim 1,wherein the pressure is between about 10 millitorr and about 250 torr.5. (canceled)
 6. (canceled)
 7. The method according to claim 1, wherein:the temperature is between about 120° C. and about 170° C.; and thepressure is between about 10 millitorr and about 1 torr.
 8. The methodof claim 1, wherein the polymer precursor comprises an organic acid. 9.The method according to claim 8, wherein the organic acid is lacticacid, itaconic acid or citric acid.
 10. The method of claim 1, whereinthe dispersed-phase precursor comprises an inorganic material.
 11. Themethod according to claim 10, wherein the inorganic material comprisesclay, talc, aluminum trihydrate, barium sulfate, a metal oxide or asilicate.
 12. The method according to claim 10, wherein the inorganicmaterial comprises clay.
 13. The method according to claim 11, whereinthe metal oxide is titanium dioxide or antimony oxide.
 14. The methodaccording to claim 11, wherein the silicate is an alumino-silicate. 15.The method of claim 1, wherein the dispersed-phase precursor comprises afibrous material.
 16. The method according to claim 15, wherein thefibrous material comprises wood fiber, flax, cotton, hemp, jute,nanocellulose, rayon, polyester, nylon, aramid fibers, rock wool,mineral wool, asbestos or fiberglass.
 17. The method according to claim15, wherein the fibrous material comprises nanocellulose.
 18. The methodof claim 1, wherein the liquid comprises water.
 19. The method of claim1, wherein the reaction product is water.
 20. The method of claim 1,further comprising treating the composite material with a cross-linkingagent.
 21. The method according to claim 20, wherein the cross-linkingagent comprises ammonium zirconium carbonate, potassium zirconiumcarbonate, a glyoxal, an aliphatic epoxy resin, a melamine formaldehyderesin or a blocked isocyanate.
 22. The method according to claim 20,wherein the cross-linking agent comprises ammonium zirconium carbonate,potassium zirconium carbonate, or glyoxal.
 23. The method of claim 1,further comprising blending the mixture with a light-scatteringcompound.
 24. The method of claim 1, further comprising blending themixture with a light-absorbing compound.
 25. The method of claim 1,further comprising blending the mixture with a fluorescent compound. 26.The method of claim 1, further comprising blending the mixture withlow-density material.
 27. A composite material produced by the method ofclaim 1.